The electronics industry has recently sought low dielectric materials, for use in fabricating very fine dimensioned integrated circuits, such as polymers may exhibit. However, the need for materials compatibility and dimensional stability over a wide range of conditions not only during ultimate end use, but also during further processing conditions leading to the finished integrated circuits, have presented a significant problem. The problem has been to make a polymeric thermoset system. This problem has been a very difficult one to solve, particularly for high Tg polymers where the desired temperature for reaction (cure) is in the range of 200-450.degree. C.
Therefore, there is a need in the electronic fabrication industry for the replacement of silica-based, interlayer dielectric materials with materials of lower dielectric values. Silica and its modified versions have dielectric values on the order of 3.0 to 5.0 and usually 4.0 to 4.5. Polymeric materials used as replacements for silica as interlayer dielectric materials can have values for dielectric constant in the range of 1.9 to 3.5, which values are highly dependent on the structure of the polymeric materials. To successfully replace silica as an interlayer dielectric material, the properties of polymeric materials must conform to the rigid manufacturing requirements for integrated circuits or microchips in the electronic fabrication industry. Crosslinking has been recognized as one way to address the requirements of electronic materials polymers.
Past attempts utilized the phenylethynyl group as a site for crosslinking polymers. Various literature on the use of the phenylethynyl group for crosslinking polymeric materials exist, as set forth below.
Hedberg, F. L.; Arnold, F. E.; J. Polym. Sci., Polym. Chem. Ed. (1976) 14, 2607-19; and Banihashemi, A.; Marvel, C. S.; J Polym. Sci., Polym. Chem. Ed. (1977) 15, 2653-65, report the preparation of polyphenylquinoxalines with pendant phenylethynyl groups and their thermal cure via intramolecular cycloaddition and the heating of the 2,2'-di(phenylethynyl)biphenyl moiety to produce a 9-phenyldibenz[a,c]anthracene moiety, which enhances the Tg of the polymer.
Hergenrother, P. M.; Macromolecules (1981) 14, (4) 891-897; and Hergenrother, P. M.; Macromolecules (1981) 14, (4) 898-904 report on the preparation of poly(phenylquinoxalines) containing pendent phenylethynyl groups along the backbone, where these materials were prepared for evaluation as precursors for high thermally stable thermosets.
Paul, C. W.; Schulz, R. A.; Fenelli, S. P.; U.S. Pat. No. 5,138,028 (1992) and Paul, C. W.; Schulz, R. A.; Fenelli, S. P.; Eur. Pat. Appl. EP 443352 A2 910828 claim the preparation of polyimides, polyamic acids, polyamic acid esters, polyisoimides which are end-capped with diarylacetylenes. The cured products are used for encapsulation of electronic devices, as adhesives, and as moldings.
Babb, D. A.; Smith, D. W.; Martin, S. J.; Godshalx, J. P. WO 97/10193 discloses various multi-phenylethynyl compounds. These materials are claimed to be used for coating a wide variety of substrates such as dielectric coatings, computer chips.
Zhou, Q.; Swager, T. M.; Polym. Preprint (1993) 34(1), 193-4, reports the preparation of all carbon ladder polymers via cyclization reactions of acetylenes.
Mercer, F. W.; Goodman, T. D.; Lau, A. N. K.; Vo, L. P, U.S. Pat. No. 5,179,188 (1993) assigned to Raychem Corp, claims polymers (oligomers) of U.S. Pat. No. 5,114,780 (1992) which are end-capped with reactive groups having double and triple bonds.
Mercer, F. W.; Goodman, T. D.; Lau, A. N. K.; Vo, L. P., WO 91/16370 (1991) claim crosslinkable fluorinated aromatic ether compositions.
Lau, K; Hendricks, N.; Wan, W.; Smith, A.; PCT/US96/10812, report the preparation of phenylethynylated monomers for use in preparing polymers which can thermally crosslinked.
U.S. Pat. No. 5,658,994 to Burgoyne, Jr., et. al. discloses the utility of poly(arylene ethers) as low dielectric interlayers for the electronics industry where the poly(arylene ether) may be crosslinked either by crosslinking itself, through exposure to temperatures of greater than approximately 350.degree. C., or by providing a crosslinking agent as well as end capping the polymer with known end cap agents, such as phenylethynyl, benzocyclobutene, ethynyl and nitrile.
Giuver, Michael D.; Kutowy, O.; ApSimon, John W.; Functional Group Polysulphones By Bromination-metalation; Polymer, June 1989, Vol 30, pp 1137-1142, describes the functionalization of polysulfones using n-butyllithium. Various functional groups were reacted, including methyl groups and benzophenone groups.
U.S. Pat. No. 4,999,415 to Guiver, et. al., discloses the functionalization of polysulfones with acetaldehyde, benzaldehyde, benzophenone, methylethylketone, phenylisocyanate, dimethyldisulfide, acetonitrile, benzonitrile, carbon dioxide, sulfur dioxide, deuterium oxide, methyl halides, allyl halides, benzyl halides, trimethylsilyl chloride, dimethylacetamide and iodine.
Guiver, Michael, D.; Croteau, S.; Hazlett, John D.; Kutowy, O.; Synthesis and Characterization of Carboxylated Polysulfones; British Polymer Journal; Vol 23; Nos 1 & 2, 1990, pp 29-39; describe the formation of carboxylated polysulfones by a lithiation/carboxylation modification procedure.
Yoshikawa, Masakazu; Hara, Hirohisa; Tanigaki, Masataka; Guiver, Michael; Matsuura, Takeshi; Modified Polysulphone Membranes: 1. Pervaporation of Water/Alcohol Mixtures Through Modified Polysulphone Membranes Having Methyl Ester Moiety; Polymer, 1992, Vol. 33, No. 22, pp 4805-4813; describe polysulphones modified with methyl carboxylates using lithiation and esterification reactions.
Yoshikawa, Masakazu; Hara, Hirohisa; Tanigaki, Masataka; Guiver, Michael; Matsuura, Takeshi; Modified Polysulphone Membranes: II. Pervaporation of Acqueous Ethanol Solutions Through Modified Polysulphone Membranes Bearing Various Hydroxyl Groups; Polymer Journal, 1992, Vol. 24, No. 10, pp 1049-1055; describe polysulphones modified with various aldehydes and ketones including benzophenone. Modification is conducted by lithiation using n-buyllithium.
Reactions of polysulphone under lithiation conditions are relatively favorable in comparison to poly(arylene ethers), as will be discussed with regard to the present invention below.
However, despite the art demonstrating various attempts to provide appropriate crosslinking of polymers for low dielectric interlayers, the art has still failed to solve the problem of thermally cured graft polymers with essentially no functional groups which have low dielectric constant and dimensional stability upon thermal crosslink as will be set forth with regard to the present invention.